Resonant network fluid level sensor assembly

ABSTRACT

A sensing assembly senses liquid levels in a reservoir and creates a sensing signal. The sensing assembly includes a first electrical conductor and a second electrical conductor extending into the reservoir. A first electrode is electrically connected to the first electrical conductor. A second electrode is electrically connected to the second electrode conductor. The sensing assembly also includes a plurality of equidistantly spaced plates that are operatively connected to the second electrode. Each of the plurality of plates combines with the first electrode to create a capacitance such that the sensing signal generating by the sensing assembly determines the level of the liquid in the reservoir. The plates, an inductor and resistors are connected together in series with each of the groupings being connected in parallel to each other along the second electrode length. The sensing signal will generate spikes that, based on amplitude, will identify the amount of a liquid in the reservoir.

BACKGROUND ART

1. Field of the Invention

The invention relates to fluid level sensing assemblies. More particularly, the invention relates to resonant fluid level sensing assemblies capable of accurately determining the level of a fluid within a reservoir by analyzing the resonance of the output signal of the fluid level sensing assembly.

2. Description of the Related Art

The storage and delivery of liquids is an important feature of many mechanisms. In an automotive environment, proper delivery of liquids is essential for the functioning and maintenance of a motor vehicle. By way of example, a motor vehicle will not function without fuel, typically liquid gasoline. That same motor vehicle will not function properly without the proper amount of oil stored in the internal combustion engine allowing it to lubricate and cool itself. These are just two fluids in a particular environment that require close observation to make sure its host mechanism, i.e., the motor vehicle, can operate properly.

Currently, there are a number of ways in which a fluid level may be measured. The mechanisms used to measure the fluid level help determine if more fluid is required in order to continue the proper maintenance and operation of the host mechanism. Fluid level measuring mechanisms include floating arm mechanisms, pressure sensors, capacitive sensors, and ultrasonic sensors. The most commonly used fluid level measuring system is the floating arm mechanism.

The floating arm mechanism is an imperfect mechanism for several reasons. First, the floating arm mechanism requires moving parts inside a liquid-filled container. This requires increased time to install the floating arm mechanism and seal it and the container or reservoir. Resistive strips used by the floating arm mechanism are susceptible to contamination and can develop contact problems. The contamination and contact problems result in erroneous measurements. Looking forward, the floating arm fluid measuring mechanism will not be able to differentiate between different types of liquids within the same reservoir. This problem will increase in the automotive environment as different types of fuels will be accepted by each motor vehicle resulting in the stratification of the fluids within a particular reservoir.

Another reason the floating arm mechanisms are inferior is that they measure liquid levels inefficiently when the reservoir holding the liquid is unusually shaped. Oftentimes when a motor vehicle is an all-wheel drive vehicle, an extra drive shaft is required to extend along the underbody of the motor vehicle. The extra shaft typically extends through the space used by the fuel tank. Therefore, the fuel tank must be modified resulting in an unusually shaped fuel tank. Multiple floating arm mechanisms are required to get accurate readings from these unusually shaped fuel tanks. This adds considerable costs to the fuel tank construction.

SUMMARY OF THE INVENTION

A sensing assembly senses liquid levels in a reservoir and creates a sensing signal. The sensing assembly includes a first electrical conductor extending into the reservoir. A second electrical conductor also extends into the reservoir and is disposed from the first electrical conductor a predetermined distance. A first electrode is electrically connected to the first electrical conductor. The first electrode extends between a first conductor end and a first distal end and has a first electrode length. A second electrode is electrically connected to the second electrical conductor. The second electrode is spaced apart from the first electrode and extends between a second conductor end and a second distal end and has a second electrode length. The sensing assembly also includes a plurality of plates that are operatively connected to the second electrode. The plurality of plates are spaced equidistantly along the second electrode length. Each of the plurality of plates combines with the first electrode to create a capacitance such that the sensing signal generated by the sensing assembly determines the level of the liquid in the reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a side view of one embodiment of the invention in a reservoir, shown in cross section, that is partially filled with a liquid;

FIG. 2 is an electrical schematic of one embodiment of the invention;

FIG. 3 is a graphic representation of an output of the sensing assembly when the reservoir is empty; and

FIG. 4 is a graph representation of an output of the sensing assembly when the reservoir has some liquid therein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the invention, a sensing assembly, is generally indicated at 10. The sensing assembly senses liquid levels in a reservoir 12. The sensing assembly 10 creates a sensing signal 54 (shown in FIGS. 3 and 4) to identify a level 14 that the liquid 16 is at within the reservoir 12. A sensing assembly 10 is designed such that it is presumed that air 18 fills the portion of the reservoir 12 that the liquid 16 does not. While it is contemplated that the embodiment shown in the Figures illustrates a sensing assembly 10 for a fuel tank 12 of a motor vehicle, it should be appreciated that the reservoir 12 may be any reservoir designed to hold a liquid 16 therein.

The reservoir 12 includes a bottom surface 13 that defines a normal 15 extending up therefrom. In the instance when the bottom surface 13 does not extend through a single plane parallel to the horizon, the normal 15 will be treated as though it is extending normal to the horizon. Therefore, the surface of the liquid 16 is always perpendicular to the normal 15.

A sensing assembly includes a base 20. The base 20 is a rectangular piece of material that is capable of having electronics fixedly secured thereto. In addition, the base 20 is fabricated of a material that does not corrode with exposure to either air 18 or the liquid 16 contemplated to be stored within the reservoir 12. The base 20 is mountable to a side 21 of the reservoir 12 allowing it to be secured in a predetermined position within the reservoir 12.

The sensing assembly 10 also includes a first electrical conductor 22 and a second electrical conductor 24. The first 22 and second 24 electrical conductors extend into the reservoir 12. These electrical conductors 22, 24 allow the sensing assembly 10 to be connected to a control circuit (not shown) that creates a signal which is modified by the sensing assembly 10. The second electrical conductor 24 is disposed from the first electrical conductor 22 a predetermined distance. It should be appreciated by those skilled in the art that the lead configuration for the electrical conductors 22, 24 may change at some point within the reservoir 12 based on design requirements.

Extending down along the base 20 is a first electrode 28. The first electrode 28 is electrically connected to the first electrical conductor 22. The first electrode 28 extends between a first conductor end 30 and a first distal end 32. The first electrode 28 defines a first electrode length 34 extending therebetween. As is shown in FIG. 1, the first electrode 28 is an elongated, continuous plate of conductive material wherein the first electrode length 34 is greater than its width.

The sensing assembly 10 also includes a second electrode 36. The second electrode 36 is electrically connected to the second electrical conductor 24. The second electrode 36 is an elongated conductor that extends between a second conductor end 38 and a second distal end 40. The second electrode 36 is spaced apart from the first electrode 28. The second electrode 36 defines a second electrode length 42 that extends between the second conductor end 38 and the second distal end 40. The second electrode 36 also is fixedly secured to the base 20 and extends therealong.

A plurality of plates 44 extend along the base 20 and are fixedly secured thereto. The plurality of plates 44 are positioned between the first electrode 28 and the second electrode 36. Each of the plurality of plates 44 are equal in size and are coplanar. Each of the plurality of plates 44 is operatively connected to the second electrode 36 such that each of the plurality of plates 44 is electrically connected to the second electrode 36. This electrical connection includes an inductor 46 and a resistor 47. The inductors 46 and resistors 47 are connected between each of the plurality of plates 44 and the second electrode 36 such that the inductors 46, resistors 47 and the plurality of plates 44 are connected in series with respect to the second electrode 36. The resistors 47 are shown in the Figures as discrete elements. It should, however, be appreciated by those skilled in the art that the plates 44, inductors 46 and second electrode 36 may be designed to incorporate the necessary resistance therein, thus obviating the need for a discrete resistive element.

In operation, the sensing assembly 10 uses each of the plurality of plates 44 and the first electrode 28 to create a plurality of capacitances by having the first electrode 28 act as a plurality of first plates 48 (FIG. 2) and each of the plurality of plates 44 acting as second plates 49 for capacitors 50. A signal is generated by a signal generator 52 and the control circuit identifies the level 14 of the liquid 16 by how the signal generated by the signal generator 52 is modified by the sensing assembly 10. This operation will be discussed in greater detail subsequently.

Referring to FIG. 3, a graph representing the sensing signal 54 as seen by the control unit is shown. In the example of the embodiment shown in FIGS. 1 and 2, there are 32 capacitors 50 created between the first electrode 28 and each of the 32 plurality of plates 44. It should be appreciated that any number of capacitors 50 may be created based on the design specifications and the accuracy requirements for a particular reservoir 12.

Returning attention to FIG. 3, there is a single spike 56. This spike 56 is the magnitude of the voltage response based on a particular voltage frequency input. This spike 56 represents all of the capacitors 50 together as they all are surrounded by the same material, e.g., air. This spike 56 is comparable to a calibration as it is the default value when the reservoir 12 is void of liquids.

Referring to FIG. 4, it can be seen that the spike 56 of FIG. 3 is reduced in magnitude. The reduction in size (dashed spike 56) is a result of fewer capacitors 50 being surrounded by air. The capacitors 50 that are not surrounded by air are surrounded by the liquid 16 that is entering the reservoir 12. The presence of the liquid 16 causes the capacitors 50 to create a different output, as is represented by a second spike 58. The different output is due to the different dielectric of the liquid 16, which creates the different output by the capacitors 50. As more liquid 16 is added to the reservoir 12, the spike 58 associated therewith will grow and the spike 56 associated with the air 18 in the reservoir 12 will continue to decrease in magnitude.

The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.

Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described. 

1. A sensing assembly for sensing liquid levels in a reservoir and for creating a sensing signal therefor, said sensing assembly comprising: a first electrical conductor extending into the reservoir; a second electrical conductor extending into the reservoir and disposed from said first electrical conductor a predetermined distance; a first electrode electrically connected to said first electrical conductor, said first electrode extending between a first conductor end and a first distal end and defining a first electrode length therebetween; a second electrode electrically connected to said second electrical conductor, said second electrode spaced apart from said first electrode and extending between a second conductor end and a second distal end defining a second electrode length therebetween; a plurality of plates operatively connected to said second electrode spaced equidistantly therealong, each of said plurality of plates combine with said first electrode to create a capacitance such that the sensing signal generated by said sensing assembly determines the level of the liquid in the reservoir; a plurality of inductors operatively connected between each of said plurality of plates and said second electrode; and a plurality of resistors operatively connected to each of said plurality of plates and said plurality of inductors such that each of said plurality of resistors, inductors and plates are connected in series with said second electrode.
 2. A sensing assembly as set forth in claim 1 wherein each of said plurality of plates extends out from said second electrode toward said first electrode.
 3. A sensing assembly as set forth in claim 2 wherein said first electrode and said plurality of plates are coplanar.
 4. A sensing assembly as set forth in claim 3 wherein each of said plurality of plates is equal in size.
 5. A sensing assembly as set forth in claim 4 wherein said first electrode is spaced from each of said plurality of plates equidistantly. 